Ancient Roman units of measurement

Ancient Roman units of measurement
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ancient_Roman_units_of_measurement".

The ancient Roman units of measurement were built on the Hellenic system with Egyptian, Hebrew, and Mesopotamian influences. The Roman units were comparatively consistent and well documented.

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1 Length
2 Area
3 Volume
- 3.1 Liquid measures
- 3.2 Dry measures
4 Mass and coins
5 Time
6 References
7 See also

Length

Modern metrologists have found the Roman foot to be ¹⁶⁄₂₈ of the Nippur cubit.

Roman unit	Latin name	Feet	Equivalence
one digit	digitus	¹⁄₁₆	18.5 mm
one inch	uncia	¹⁄₁₂	24.6 mm
one palm	palmus	¹⁄₄	74 mm
one foot	pes	1	296 mm
one cubit	cubitus	1+¹⁄₂	444 mm
one step	gradus	2+¹⁄₂	0.74 m
one pace	passus	5	1.48 m
one perch	pertica	10	2.96 m
one arpent	actus	120	35.5 m
one stadium	stadium	625	185 m
one mile	milliarium	5000	1.48 km
one league	leuga	7500	2.22 km

Notes

From late Antiquity the Roman foot was sometimes divided into unciae comprising 12 equal parts.
The ancient digit measure, however, largely dominated before the beginning of the Middle Ages.
The value of the historical Roman foot scientifically obtained through modern statistical methods is 296.2 mm ± 0.5 mm, or about (296.2 ±0.17%) mm (cf. Rottländer, Tübingen, Germany). The table above is based on this value, but rounded to the millimetre precision for the foot.
The widely accepted ratio between the Roman foot and the English foot is 36:35. The latter one is 16/28 Mesopotamian cubit and the ratio between this one and the Roman cubit is 20:24. If the present English foot is taken as for reference, the Roman foot should be 296 1/3 mm. That is within the margin obtained by R.C.A. Rottländer (see references).
A Roman foot can be visualised as being approximately equal to the height of an A4 sheet of paper. This comparison, although descriptive, is +0.27% out of the range given above.

Area

Roman unit	Latin name	Acres	Equivalence
one square foot	pes quadratus	¹⁄_{14 400}	~ 876 cm²
one square perch	scripulum	¹⁄₁₄₄	~ 8.76 m²
one aune of furrows	actus minimus	¹⁄₃₀	~ 42 m²
one rood	clima	¹⁄₄	~ 315 m²
one acre	actus quadratus also known as acnua	1	~ 1260 m²
one yoke	iugerum	2	~ 2520 m²
one morn	heredium	4	~ 5040 m²
one centurie	centurium	400	~ 50.5 ha
one "quadruplex"	saltus	1600	~ 201.9 ha

The Roman acre is the squared Roman arpent, 120 pedes by 120 pedes. This equals 14 400 square feet or about 0.126 hectares.

The Romans also had a unit of area called a quinaria, which was used to measure the cross-sectional area of pipes. One quinaria was considered to be roughly 4.2 cm².

Note: Some researchers assert that the Roman surveyors used a perch of ten Greek "Pous of Kyrenaika", i.e. 3.087 m instead of the perch of ten of their own feet, equal 2.964 m.
According to this hypothesis – currently not supported by the majority of modern metrologists – all the Roman area measures should be multiplied by 625/576, i.e. 8.5 % larger.
If the irrefutable proof for the real existence of a Roman surveyor perch of 10 Roman feet 6⅔ digits can be adduced, then the saltus equates to one Roman square mile exactly.

Volume

Liquid measures

Roman unit	Latin name	Sesters	Equivalence
one spoonful	ligula	¹⁄₄₈	~ 1+¹⁄₈ cl
one dose	cyathus	¹⁄₁₂	~ 4+¹⁄₂ cl
one sixth-sester	sextans	¹⁄₆	~ 9 cl
one third-sester	triens	¹⁄₃	~ 18 cl
one half-sester	hemina	¹⁄₂	~ 27 cl
one double third-sester	choenix	²⁄₃	~ 36 cl
one sester	sextarius	1	~ 54 cl
one congius	congius	6	~ 3+¹⁄₄ l
one urn	urna	24	~ 13 l
one jar	amphora	48	~ 26 l
one hose	culleus	960	~ 520 l

The Roman jar, so-called "amphora quadrantal" is the cubic foot. The congius is half-a-foot cubed. The Roman sester is the sixth of a congius.

Dry measures

Roman unit	Latin name	Pecks	Equivalence
one drawing-spoon	acetabulum	¹⁄₁₂₈	~ 6+³⁄₄ cl
one quarter-sester	quartarius	¹⁄₆₄	~ 13+¹⁄₂ cl
one half-sester	hemina	¹⁄₃₂	~ 27 cl
one sester	sextarius	¹⁄₁₆	~ 54 cl
one gallon	semodius	¹⁄₂	~ 4+¹⁄₃ l
one peck	modius	1	~ 8+²⁄₃ l
one bushel	quadrantal	3	~ 26 l

Like the jar, the Roman bushel or "quadrantal" is one cubic foot. It is almost 26.027 litres. One-third of a quandrantal is a Roman peck.

Mass and coins

Roman unit	Latin name	Drachms	Equivalence
one chalcus	chalcus	1 / 48	~ 71 mg
one siliqua	siliqua	1 / 18	~ 189⅓ mg
one obolus	obolus	1 / 6	~ 0.568 g
one scruple	scrupulum	1 / 3	~ 1.136 g
one dram	drachma	1	~ 3.408 g
one shekel	sicilicus	2	~ 6.816 g
one ounce	uncia	8	~ 27.264 g
one pound	libra	96	~ 327.168 g
one mine	mina	128	~ 436.224 g

The Roman pound is exactly three quarters of the Greek mine.
Thus the Greek and Roman drachm is related by the ratio 32 to 25.

All the multiples of the Roman ounce have their own names
1 ounce =	uncia	7 ounces =	septunx
2 ounces =	semis	8 ounces =	bes
3 ounces =	triens	9 ounces =	dodrans
4 ounces =	quadrans	10 ounces =	dextans
5 ounces =	quincunx	11 ounces =	deunx
6 ounces =	sextans	12 ounces =	as

One and a half ounces was called by Romans "sescuncia". Some of these nouns were used to designate Roman bronze coins.

Time

The Julian calendar was introduced in 45 BC replacing the earlier Roman calendar. In the Julian calendar as in the Gregorian calendar an ordinary year is 365 days long and a leap year is 366 days long. The difference is which years are leap years. In the Julian calendar every fourth year is a leap year. The Gregorian calendar uses a more complex algorithm to more closely approximate the length of the tropical year.

References

Vormetrische Längeneinheiten by Rolf C. A. Rottländer, Rottenburg / Köln (also see Search-Engine).
Recovery of the Ancient System Foot/Cubit/Stadion by Dieter Lelgemann, acting Director of the Institute for Geodesy and Geo-Information Technology, TU Berlin.
On the Ancient Determination of Meridian Arc Length by Eratosthenes of Kyrene Dieter Lelgemann, WS – History of Surveying and Measurement, Athens, Greece, May 22-27, 2004.
Knobloch, Eberhard, Dieter Lelgemann und Andreas Fuls: "Zur hellenistischen Methode der Bestimmung des Erdumfangs und zur Asienkarte des Klaudios Ptolemaios.", published in zfv (Zeitschrift für Geodäsie, Geoinformation und Landmanagment) 128. Jahrgang, Heft 3/2003, S. 211-217.
Reference draws of the Nippur Cubit at Florencetime.net.
Proposal to Add Ancient Roman Weights and Monetary Signs to UCS (Universal Character Set)

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